1. Field of the Invention
This invention relates to new and improved catalysts for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid.
2. Background Information Including Description of Related Art
It is known to produce vinyl acetate by reaction of ethylene, oxygen and acetic acid using a catalyst consisting of palladium and gold supported on a carrier. While the process utilizing such a catalyst is capable of producing vinyl acetate at relatively high levels of productivity, any expedient resulting in even greater productivity would be very desirable.
The following references may be considered material to the invention claimed herein.
U.S. Pat. Nos. 3,775,342 issued Nov. 27, 1973, and 3,822,308 issued Jul. 2, 1974, both to Kronig et al., each discloses a method of making vinyl acetate catalysts comprising treating a support simultaneously or successively with a solution A containing dissolved salts of noble metals such as palladium and gold and a solution B containing compounds able to react on the support with the noble metal salts to form water insoluble compounds, treating such water-insoluble compounds with a reducing agent to convert the water-insoluble noble metal compounds to the free metals, washing the catalyst to remove water-soluble compounds, and applying an alkali metal compound e.g. an alkali metal carboxylate before or after treatment with the reducing agent. Solution A can optionally also contain salts of other metals such as magnesium, calcium, barium and rare earths.
U.S. Pat. No. 5,332,710, issued Jul. 26, 1994, to Nicolau et al., discloses a method of preparing a catalyst useful for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid, comprising impregnating a porous support with water soluble salts of palladium and gold, fixing the palladium and gold as insoluble compounds on the support by immersing and tumbling the impregnated support in a reactive solution for at least 1/2 hour to precipitate such compounds, and subsequently reducing the compounds to its metallic form.
U.S. Pat. No. 5,567,839, issued Oct. 22, 1996, to Gulliver et al., discloses a method of producing vinyl acetate catalysts including the step of using a barium "salt", such as barium hydroxide, to precipitate water-insoluble palladium and gold compounds onto a support prior to reduction with a reducing agent. When barium hydroxide is used as precipitant, residual barium remains in the finished catalyst.